1. Field of the Invention
The present invention relates generally to grounding devices and more particularly to an improved low impedance grounding cone for the peripheral grounding of a coaxial cable to protect electronic functions aboard Naval ships in the presence of an electromagnetic pulse or any electromagnetic interference source having a similar frequency range.
2. Description of the Prior Art
An electromagnetic pulse, hereinafter (EMP), is an electrical signal of large amplitude and broad frequency range (0.1 MHz to 10 MHz) that is generated by a nuclear weapon at the time of detonation. An EMP may be present when all other nuclear weapon effects are absent and may upset or damage electronic equipment over a wide geographic area. The discussion hereintofollow applies to any electromagnetic interference source within the above frequency range.
The cable shield grounding technique for EMP protection presently used on most operational fleet ships is described in MIL-STD-1310C (Navy), Nov. 30, 1973, page 29. The technique essentially involves placing a metal hose clamp around the bared shield of a coaxial cable with an attached grounding strap having one end welded to the clamp and the other end welded to the hull or bulkhead of the ship. These grounding straps are from 6 to 12 inches long and, thus, exhibit a high inductance (high impedance) path to ground for the high frequency components present in externally induced currents in the shield from an EMP source. Consequently, there is a need in the prior art to improve attenuation of all frequency components of externally induced currents in the shield from an EMP source and especially the high frequency components.
Another cable shield grounding technique has been specified for use on operational fleet ships and is described in the most recent MIL-STD-1310D (Navy), Feb. 8, 1979, page 32. This technique includes installing a kickpipe through the ship's hull or bulkhead into a compartment. A grounding ring or sleeve is disposed over the bared shield of the coaxial cable when it is pulled through the kickpipe into the compartment. Then a lower nut is tightened about the grounding ring, bared shield of the coaxial and a threaded end of the kickpipe. This technique is an improvement over the grounding system, aforementioned, since it allows 360.degree. grounding and decreases high frequency components of externally induced EMPs. Nevertheless, it does not provide for simple retrofitting of existing grounding systems, especially those with kickpipes mounted flush with the non-weather or compartment side of the ship's hull. Consequently, there is a need in the prior art to attenuate high frequency components of externally induced EMPs to levels heretofore unattainable, while simplifying retrofitting of the foregoing types of grounding systems on operational fleet ships.